Liver transplantation (LTx) is accepted therapy for various liver diseases. However, there are two problems: primary nonfunction (PNF) and shortage of livers. PNF, caused by preservation or reperfusion injury, necessitates a retransplant. This contributes to the shortage of livers. PNF contributes to the enormous cost of LTx and significant patient discomfort. Improving preservation of the liver would contribute significantly to improved results in LTx. Our goals in this project are to improve liver preservation to reduce PNF, decrease cost, decrease shortage of livers and deaths on the waiting list, provide a method to judge viability of the liver, and increase utilization of marginal livers (ischemic). We hypothesize that significant improvements in liver preservation will require continuous hypothermic machine perfusion (HMP). We shall demonstrate the feasibility of excellent quality, long-term liver preservation by HMP accomplishing these five specific aims: 1) optimize the method of liver perfusion, 2) optimize the perfusate specifically for the liver, 3) enhance preservation with cytoprotective agents previously shown to decrease liver injury, 4) develop a viability assay based on liver hypothermic metabolism, and 5) optimize HMP of the liver to salvage marginal (ischemically injured) livers. How these research strategies affect the quality and longevity of liver preservation will be judged by survival in the orthotopic rat liver transplant model (OLTx) and the degree of metabolic injury.using the isolated perfused liver (IPL). Integrity of the microvascular system and sinusoids will be assessed by electron microscopy. Strategies that show significant enhancement of rat liver preservation will be confirmed in the dog liver Tx model. The new information generated will lead to a more comprehensive understanding of liver preservation/reperfusion injury, develop a new state-of-the-art for liver preservation, provide measures of liver viability during HMP, and increase the donor pool by salvaging marginal livers. Successful HMP could have a dramatic effect on the outcome of clinical LTx and become the technique of choice in large transplant centers such as ours.